Vital signs of a subject, for example the heart rate (HR), the respiration rate (RR) or the body temperature serve as indicators of the current health status of a person and as powerful predictors of serious medical events. For this reason, vital signs are extensively monitored in in-patient and out-patient care settings, at home or in further health, leisure and fitness settings.
US 2009/0204100 A1 discloses a body cover comprising a temperature sensing element. The temperature sensing element senses the temperature of proximate skin and converts the locally sensed temperature into a visual and/or electrical signal. The body cover may include a local display for converting electrical signals that are output by temperature sensing elements into a visual signal such that a wearer or a camera can read the state of the skin from the body cover.
U.S. Pat. No. 4,945,919 discloses a rhinological diagnostic device comprising a thermochromic liquid crystal layer for displaying a temperature distribution of expired air in a thermochromic pattern for diagnosing an abnormality in the nasal cavity.
US 2012/0289850 A1 discloses monitoring respiration of a subject with a thermal imaging system set to a temperature range of a facial region. A thermal camera operating in the infrared wavelength range of 7,500 nm to 14,000 nm captures a thermal image video sequence. Temperatures of extremities of the head and face are used to locate facial features in the captured thermal images, i.e., nose and mouth, which are associated with respiration. Since the temperature of the exhaled air typically has a higher temperature than the inhaled air, a temporal variation of the nose and mouth region can be evaluated to determine the respiration rate. In an alternative embodiment, the respiration rate is determined by the motion of the nostrils, lips or chest.
US 2012/0052469 A1 discloses a nasal flow controller device. An air flow during sniffing-in cools a region about the nose and air-flow during sniffing out warms a region about the nose. A pad can be attached to the subject's nose which responds sufficiently fast to temperature variations. A camera again senses the temperature variations.
A disadvantage of such systems is that a thermal measurement only works if there is a significant temperature difference between environmental temperature and exhaled air temperature. A further disadvantage is that thermal cameras are expensive. Furthermore, additional measurement modalities are needed to measure additional vital signs like the heart rate or oxygen saturation in parallel.
As an alternative to thermal imaging, U.S. Pat. No. 6,110,123 A discloses motion-based respiration measurement. A prerequisite for this technique is that respiration correlated movements must be visible for the camera system. Preferentially, a movement of the chest is observed since respiratory movements are usually not visible in the face. However, for example in a hospital setting where the patient is lying in bed and covered with a blanket, only a very limited respiratory movement can be observed. Furthermore, a chest movement does not guarantee a gas flow into the lungs. Furthermore, a motion-based respiration measurement is susceptible to motion artifacts.